As a system that provides a multipoint conference service, there is a multipoint teleconference system disclosed in Japanese Patent Laid-Open No. 2000-175170. This multipoint teleconference system includes plural conference terminals and a multipoint control apparatus to which these conference terminals are connected. The conference terminals are allocated to participants.
In this multipoint teleconference system, the respective conference terminals transmit acoustic signals concerning sound detected by the conference terminals to the multipoint control apparatus. The multipoint control apparatus adds up the acoustic signals received from the respective conference terminals. For each of the conference terminals, the multipoint control apparatus subtracts the acoustic signal, which is received from the conference terminal, from the added-up acoustic signal, encodes an acoustic signal obtained as a result of the subtraction, and transmits the encoded acoustic signal to the conference terminal.
The multipoint control apparatus can be applied to various communication networks such as a line switching network, a mobile network, and a packet network. In the line switching network, communication protocols specified by H.323 and H.324 of the ITU-T (Telecommunication Union Telecommunication Standardization Sector) recommendation are used. In the mobile network, a communication protocol specified by 3G-324M is used. In the packet network based on the IP (Internet Protocol), RFC3550RTP of the IETF (The Internet Engineering Task Force) is used. “RFC” is an abbreviation of “Request for Comments” and “RTP” is an abbreviation of “Real-time Transport Protocol”.
As the multipoint control apparatus, there are a multipoint control apparatus that is mounted with a sound encoder for telephone band sound and a multipoint control apparatus mounted with a sound encoder for wideband sound. The sound encoder for telephone band sound has a sampling frequency of 8 kHz and that employs a 3.4 kHz band to transmit a sound signal. The sound encoder for wideband sound has a sampling frequency of 16 kHz and employs a 7 kHz band to transmit a sound signal. As a sound encoder for telephone band sound, a sound encoder of an AMR (Adaptive Multi-Rate) system adopted in G.711, G.729, and 3GPP of the ITU-T recommendation, a sound encoder of an EVRC (Enhanced Variable Rate Codec) system adopted in 3GPP2 of the ITU-T recommendation, and the like are used. As a sound encoder for wideband sound, a sound encoder of an AMR-WB (Wide Band) system specified by G.722 and 3GPP TS26.190 of the ITU-T recommendation is used. It is possible to handle sound signals in a wider band by using the codec of an MPEG-4AAC (Advanced Audio Coding) or the like.